Hearing loss affects over 10% of the North American population, with over 8% of this group suffering from profound deafness. Tinnitus, described as “hissing, roaring or ringing” in the ear(s) or head, is an auditory perception not produced by an external sound. In the US, as many as 50 million people are affected by tinnitus to some degree and up to 12 million have sought medical attention for the problem. About 1 million sufferers are so seriously debilitated that they cannot function on a normal, day-to-day basis.
Hearing aids, cochlear implants, and tinnitus maskers can be used to help individuals with mild to severe hearing loss, severe to profound deafness, and tinnitus, respectively. By amplifying environmental sounds, hearing aids and cochlear implants often serve the dual purpose of providing a hearing percept and masking tinnitus, for those who suffer from both conditions. A tinnitus instrument refers to a hearing aid that also provides an overlying masking noise. Tinnitus instruments are used for hearing impaired tinnitus sufferers who do not obtain sufficient tinnitus relief from the amplification of environmental sounds alone.
The aforementioned devices used to treat hearing loss and/or tinnitus can be worn, at least in part, externally on the body in the area of the ear. As a result, these devices can stigmatize the wearer and therefore lead to device rejection. For example, the penetration rate of hearing aids in the US is only about 20% due, in part, to patient-related limitations such as stigma and vanity (Sweetow, R. W., “An Analysis of Entry-Level, Disposable, Instant-Fit and Implantable Hearing Aids”, The Hearing Journal, 54(2), 2001).
Various prior art describes partially or fully implantable devices that induce a hearing percept via bone conduction. The US FDA-approved bone-anchored hearing aid (BAHA), as described by Hakansson et al. in “Ten Years of Experience with the Swedish Bone-Anchored Hearing System”, Supplement 151, 99(10) Part 2:1-16, 1990, consists of a titanium screw, secured in temporal bone, and attached percutaneously to a vibrating sound processor. The BAHA, which is a commercial device sold by Entific Medical Systems of Sweden, is indicated for people with conductive or mixed hearing losses, with a bone-conducted pure-tone average of less than 60 dB HL. Although it is reported that the BAHA provides a satisfactory percept in appropriately selected patients (e.g., Lustig et al., “Hearing Rehabilitation Using the BAHA Bone-Anchored Hearing Aid: Results in 40 Patients”, Otology and Neurotology 22:328-34, 2001), it has the significant disadvantages of poor aesthetics and infection/inflammation around the implantation site. Additionally, U.S. Pat. Nos. 4,498,461; 4,612,915; and 4,904,233 describe a particular type of coupling to a bone-anchored hearing aid. In his PhD thesis, Stenfeldt describes implanting a bone-anchored hearing aid closer to the cochlea by implanting it within the mastoid bone and attaching it to a microphone either implanted in the ear canal or housed in an external unit (Stenfeldt, S. “Hearing by Bone Conduction, Physical and Physiological Aspects”, Technical Report No. 358, School of Electrical and Computer Engineering, Chalmers University of Technology, Goteborg, 1999). The exact position of the bone conducting device is not specified. Stenfeldt's proposed setup also mentions an implanted rechargeable battery and electronics package and an internal coil for recharging purposes. He further mentions a similar unit, but without an implanted microphone, to be used as a totally implanted tinnitus masker. Stenfeldt's thesis provides very limited information about the implanted bone conductor; he does not provide any engineering designs, calculations, or suggestions as to how such devices could be fabricated. PCT patent WO 01/93635 A1 describes a hearing aid device of the bone conduction type that is comprised of an implantable part (vibrator) osseointegrated partly inside the skull bone, and an external part (microphone, electronic circuitry, power source). The WO 01/93635 device comprises an external and an implantable component such that the device as a whole is not entirely implantable. The vibrator of the WO 01/93635 patent is located partly outside the skull bone and at the side of the head. The WO 01/93635 device is also preferably electromagnetic and is therefore incompatible with magnetic resonance imaging (MRI).
There exists prior art that describes partially or fully implantable hearing aids that place a vibrating prosthesis on the ossicular chain in order to transmit vibrations to the cochlea. For example, U.S. Pat. No. 5,800,336, issued to Ball, et al. discloses a “floating mass transducer”, consisting of an electromagnet attached to bone within the middle ear, that delivers amplified vibrations to the inner ear. Furthermore, in U.S. Pat. No. 5,800,336, Ball, et al. note that the properties of piezoelectrics and bimorph piezoelectrics can provide a basis for floating mass transducers.
In U.S. Pat. No. 5,558,618, Maniglia describes a semi-implantable middle ear hearing device that consists of a magnet mounted to the ossicular chain that is driven by an implanted electromagnetic driving coil. Dormer, in U.S. Pat. No. 6,277,148, describes a middle ear magnet implant driven by a coil placed in the external auditory canal.
There also exists prior art that describes partially or fully implantable hearing aids that place a vibrating prosthesis directly on the otic capsule. For example, in U.S. Pat. No. 5,360,388, Spindel et al. describe an implantable hearing aid that includes an electromagnet fixed to the round window of the cochlea. In U.S. Pat. No. 5,277,694, Leysieffer, et al. describe a vibrating piezoelectric device for direct mechanical stimulation of the middle or inner ear. In U.S. Pat. No. 5,772,575, Lesinski et al. describe a fully implantable hearing aid, suitable for conductive and/or sensorineural hearing loss, that uses a piezoelectric transducer implanted adjacent to the oval window of the inner ear. In U.S. Pat. No. 5,879,283, Adams et al. describe a method and apparatus for improving the frequency response of a piezoelectric transducer in an implantable hearing system. The improvements are achieved by using different numbers of transducer elements and/or transducers of different dimensions and/or different material properties and then mounting these transducers, using different mounting techniques, to different auditory elements (e.g., ossicles, inner ear).
Most of the prior art describing fully implantable hearing aids and/or tinnitus maskers (e.g., U.S. Pat. Nos. 5,800,336; 5,558,618; 6,277,148; 5,360,388; 5,277,694; 5,772,575) have the fundamental and serious disadvantage that the surgery required for implantation of the electromechanical transducer requires mechanical manipulations on the ossicular chain or directly at the entry area of the inner ear (oval or round window) and thus involves considerable risk of middle or inner ear impairment. Furthermore, the necessary surgical opening of a sufficiently large access to the middle ear from the mastoid can involve the serious risk of facial nerve damage and the associated partial paralysis of the face. Moreover, it cannot be guaranteed that the mechanical coupling will be of a long term, stable nature or that additional clinical damage will not occur (e.g., pressure necroses in the area of the ossicles).
Various prior art attempts to circumvent some of the aforementioned disadvantages of implantable hearing aids/tinnitus maskers. In U.S. Pat. No. 5,498,226, Lenkauskas describes a totally implanted hearing device placed in the mastoid area that transfers vibrations to the cochlea, via the perilymph, by drilling a hole into the posterior semicircular canal (i.e. a fenestration), covering such hole with perichondrium or fascie, and placing a piston over the fenestration, thereby bypassing the middle ear system. Possible surgical complications of this procedure include excessive leakage of perilymph fluid, rupture of the membranous labyrinth, and serious infection of inner ear fluids. Furthermore, Lempert, J. “Fenestra Non-Ovalis: A New Oval Window for the Improvement of Hearing in Cases of Otoselerosis”, Archives of Otolaryngology, 34:880-912, 1941, describes a tendency for bone to repair itself after injury, wherein a significant percentage of fenestrated horizontal semicircular canals (i.e. 88 of 300) closed due to either bone regeneration or the formation of fibrous connective tissue. Accordingly, such bone growth will increase the stiffness of the covering over the trauma site of the fenestration, thereby attenuating the action of the vibrating piston as described in U.S. Pat. No. 5,498,226. U.S. Pat. No. 6,251,062, which describes an implantable device for treatment of tinnitus, avoids entering the middle or inner ear spaces by positioning an electroacoustic transducer in the mastoid cavity. In at least one embodiment, sound emitted from the transducer travels via the natural passage of the aditus ad antrum from the mastoid to the tympanic cavity in the area of the middle ear. This sound causes mechanical vibrations of the eardrum which travel via the mechanical transmission through the middle ear ossicles to the inner ear or via direct acoustic excitation of the oval or round window of the inner ear. U.S. Pat. No. 6,251,062 suffers from the same disadvantage as other implantable hearing aids/tinnitus maskers in that it relies on the middle ear space for transmission of sound to the inner ear. Therefore, the device(s) may not be indicated for use in patients who have non-treatable or transient middle ear pathology (e.g., otosclerosis, middle ear fluid), congenital malformations (e.g., atresia, malformed/missing ossicles) or who have had surgery affecting the mastoid or middle ear space (e.g., radical mastoidectomy).
There exists prior art describing fully implantable cochlear prostheses, for example, see U.S. Pat. No. 6,358,281 B1 and US Patent Application 2002/0019669 A1, included herein by reference, and U.S. Pat. Nos. 5,906,635; 6,272,382 B1 and 6,308,101 B1. Such prostheses are devices that stimulate the auditory nerve and are indicated for profoundly hearing impaired individuals who obtain inadequate benefit from the use of hearing aids. There is a significant number of severely hearing impaired individuals who show relatively good preservation of low frequency hearing and little or no functional hearing in the high frequency range above 1 kHz. Even with optimal acoustic amplification, speech understanding often remains very poor (monosyllabic understanding <30-40%) for these individuals. Recent data indicate that, for individuals with sufficient low-frequency hearing, the combination of acoustic and electric stimulation (in the same ear) provides additional benefit for speech understanding in comparison to electric stimulation via cochlear implantation alone (see e.g. Tillein et al., “Simultaneous Electrical and Acoustical Stimulation of the Normal Hearing Ear. Results from Acute and Chronic Experiments with Cats and Guinea Pigs”, Oral Presentation, 2001 Conference on Implantable Auditory Prostheses, Aug. 19-24, 2001; Kiefer et al., “Combined Electric-Acoustic Stimulation of the Auditory System—Results of an Ongoing Clinical Study”, Oral Presentation, 2001 Conference on Implantable Auditory Prostheses, Aug. 19-24, 2001; McDermott et al., “Combining Electric and Acoustic Hearing: Perceptual Characteristics and Improved Sound Processing”, Oral Presentation, 2001 Conference on Implantable Auditory Prostheses, Aug. 19-24, 2001; Turner & Gantz, “Combining Acoustic and Electric Hearing for Patients with high-Frequency Hearing Loss”, Oral Presentation, 2001 Conference on Implantable Auditory Prostheses, Aug. 19-24, 2001). Acoustic stimulation is typically provided to such cochlear implant recipients through the use of an acoustic hearing aid.
The prior art, describing cochlear prostheses, does not appear to allow for a totally implanted hearing aid in addition to the totally implanted cochlear prosthesis. Thus, the advantage of total implantation would be significantly diminished for those cochlear implant recipients who would benefit from the additional use of externally worn acoustic hearing aid(s).
Thus, there is need for a totally implantable, low power consuming, vibrational element (i.e. a mechanical transducer) that can provide stimulation to the cochlea. Such a transducer must be easily and safely implanted into nearly all individuals. Additionally, the surgery should be fully reversible and cause no permanent side effects. Ideally, the transducer would not rely on transmission through the middle ear space and therefore could be used for individuals with (or without) middle ear pathology. The transducer should have enough vibrational capacity to ameliorate severe hearing loss across the speech frequency range yet be flexible enough to provide sub-threshold levels of stimulation or stimulation in selected frequency regions only. The transducer could then be used as an integral part of a fully (or partially) implantable hearing aid, tinnitus masker, or tinnitus instrument. Another potential use for the transducer is in combination with a fully implantable cochlear implant for those cochlear implant candidates who gain greatest benefit from electric plus acoustic stimulation (e.g., those with severe progressive hearing loss or those who have substantial low frequency hearing but a profound loss in the higher frequencies). The transducer would provide acoustic stimulation in the frequency range where there is residual aidable hearing.